1. Field of the Invention
This invention relates to a jet flow type automatic soldering apparatus utilizing a lead-free solder for mounting a plurality of electronic parts on a printed circuit board.
2. Description of the Related Art
Conventionally in a jet flow type automatic soldering apparatus, it is common that component parts equipped in a solder bath are made from stainless steel and a Sn (Tin)xe2x80x94Pb (Lead) based eutectic solder is employed as a melting solder. A relative density of no such Snxe2x80x94Pb based eutectic solder is about 8.4 (in the case of Tin(Sn): 63% , Lead(Pb) : 37%), and this type of Snxe2x80x94Pb based eutectic solder is suitable for mounting various electronic parts on a printed circuit board because of its superior characteristics such as temperature characteristic, soldering characteristic besides its reliability as a material.
However, the above-mentioned Snxe2x80x94Pb based eutectic solder includes lead (Pb) material. In view of the world wide environmental protection, the regulation of using such lead material has been reinforcing and it becomes common to use a lead-free solder in this field. Suppose the components of the lead-free solder are 2.5 weight % of silver, 0.5 weight % of cupper, 1.0 weight % of bismuth, and the rest is tin, and in this case, a relative density of such lead-free solder becomes about 7.5.
When a conventional automatic soldering apparatus employs such lead-free solder for the sake of the environmental protection, the component parts made of stainless steel such as a nozzle plate for a jet flow solder and fastening parts such as bolts, nuts and washers for fastening the nozzle plate to a predetermined position in the solder bath are used. In this case, a relative density of these component parts, namely the relative density of the stainless steel, is about 7.9 and this is larger than the relative density of the lead-free solder, namely about 7.5 as mentioned above. Accordingly, when some pieces of the component parts are removed by chance and dropped off from the equipped positions, they would sink into a bottom of the solder bath.
As described above, when the pieces of component parts equipped in the solder bath sink into the bottom of the solder bath, it becomes very difficult to discover and to pick up these dropped component parts, and further these dropped small component parts such as bolts, nuts and washers might be swallowed in the a jet flow pump provided for generating jet stream of the melting solder. These swallowed component parts might induce the breakage of the jet flow pump and the damage of equipment of the drive section in the automatic soldering apparatus.
Accordingly, in case of using the lead-free solder in accordance with the environmental protection, there remains many problems to clear such as sinking of dropped off component parts into the bottom of the solder bath, difficulty of early detection of the dropped component parts and the breakage or damage by such dropped off component parts.
In order to overcome above mentioned problem, this invention presents an automatic soldering apparatus characterized wherein, any of the component parts equipped in the solder bath are made from material having a relative density smaller than a relative density of a lead-free solder employed in the solder bath of the automatic soldering apparatus.
According to the present invention, the component parts equipped in the solder bath include a part or all of a jet nozzle, fastening parts for the jet nozzle, adjusting component parts or the like.
In accordance with the automatic soldering apparatus of this invention, the component parts equipped in the solder bath such as a nozzle plate for jet flow solder and fastening parts such as bolt, nut and washer for fastening the nozzle plate to a predetermined position in the solder bath are made from material having a relative density smaller than the relative density of the lead-free solder. Accordingly, in case where some pieces of the component parts are dropped off in the solder bath, such dropped off component parts can be floated on the surface of the melting lead-free solder due to the relative density difference of the component parts and the lead-free solder.
Thereby, it is prevented to take long time to find out the dropped off component parts and the damage of the equipment can be avoided and it becomes easy to discover and to recover such dropped off component parts.